Power supply for battery powered devices

ABSTRACT

An auxiliary power supply ( 150 ) includes an auxiliary battery ( 152 ), power supply circuitry ( 154 ), and a connector ( 108   b ). The power supply circuitry ( 154 ) supplies an output which provides electrical energy for powering the electrical circuitry ( 102 ) of a battery powered device ( 100 ) and for recharging a battery ( 104 ) associated therewith. In one embodiment, the power supply circuitry ( 154 ) supplies an output current which is a function of the charge state of the auxiliary battery ( 152 ) and a load current presented by the electrical circuitry ( 102 ).

BACKGROUND

The present invention relates to power supplies for battery powereddevices. It finds particular application to situations in which it isdesirable to supplement the energy provided by or otherwise charge themain battery of a battery powered device with energy from an auxiliarybattery.

Recent years have seen a proliferation of battery powered devices.Digital cameras, personal digital assistants (PDAs), hand held games,portable audio players, remote controls, wireless computer keyboards andmice, portable and remote data communications devices, and mobiletelephones are but a few examples.

These devices typically include one or more main batteries which powerthe device during normal operation. Where the main batteries arerechargeable (secondary), the devices are sometimes provided withbattery charging circuitry which provides electrical energy for chargingthe batteries. Depending on the implementation, the charging circuitrymay be located either internal or external to the device itself. In anycase, the charging circuitry is ordinarily powered from an alternatingcurrent (AC) power outlet, a 12 volt direct current (VDC) automobilepower outlet, or the like. Consequently, the device must be returned toa fixed or semi-fixed location for charging.

So-called hybrid battery management technology, which uses an externalauxiliary battery together with associated charge control circuitry, hasbeen used to provide supplemental power to battery powered devices. Inone implementation, the auxiliary battery and charge control circuitryhave been housed in a generally cylindrical housing, which has beensuspended at one end of a cable, with the other end connected to thepositive and negative terminals of the charging or power port of thebattery powered device.

FIG. 1 shows the output current I_(out) provided to a device having alithium ion (Li-ion) main battery according to a hybrid batterymanagement technique. Where the main battery voltage is less than afirst value, the output current is substantially independent of the mainbattery voltage. Where the main battery voltage has a relatively highervalue, the output current is a substantially linear function of the mainbattery voltage. Where main battery voltage has had a still highervalue, the output current has again been substantially independent ofthe main battery voltage. As can also be seen in FIG. 1, the outputcurrent has also been a function of the auxiliary battery voltage.

While these techniques have provided for more convenient charging of thedevice's main battery during mobile operation, there remains room forimprovement. In particular, it remains desirable to extend the operatinglife of the auxiliary battery while minimizing modifications to thebattery powered device. In many cases, it is also desirable that theexternal device have a form factor which complements that of the batterypowered device.

SUMMARY

Aspects of the present invention address these matters, and others.

According to a first aspect of the invention, an auxiliary power supplyis adapted for use with a battery powered device including firstelectrical circuitry which presents a time varying electrical load and afirst rechargeable battery which provides electrical energy to the firstelectrical circuitry. The auxiliary power supply includes a batteryreceiving region adapted to receive a second battery, and secondelectrical circuitry. The second electrical circuitry receives a signalfrom the battery powered device. The signal is indicative of themagnitude of the time varying electrical load. The second electricalcircuitry also utilizes energy from the second battery to produce apower supply output for recharging the first rechargeable battery andfor providing electrical energy to the first electrical circuitry, andadjusts the power supply output as a function of the charge state of thefirst rechargeable battery, the charge state of the second battery, andthe signal. The auxiliary power supply also includes a first electricalconnector in operative communication with the second electricalcircuitry and adapted to selectively electrically connect the powersupply output to the battery powered device.

According to another aspect of the invention, an apparatus is adapted tosupply electrical energy to a battery powered device including a first,rechargeable battery and first electrical circuitry, wherein the firstelectrical circuitry receives electrical energy from the first batteryand presents a time varying electrical load current during operation ofthe device. The apparatus includes a first housing which defines abattery receiving region, first and second battery contacts for makingelectrical contact with a second battery received in the batteryreceiving region, a first electrical connector in mechanicalcommunication with the first housing and disposed electrically betweenthe second battery and the first electrical circuitry, and secondelectrical circuitry. The second electrical circuitry receives energyfrom the second battery, generates an output for supplying electricalenergy to the first electrical circuitry and for recharging the firstbattery, and adjusts the output as a function of the state of charge ofthe first battery and a signal indicative of the time varying electricalload current.

According to another aspect of the invention, a power supply is adaptedfor use with a battery powered device including first electricalcircuitry which presents a time varying electrical load current and afirst, rechargeable battery which supplies electrical energy to thefirst electrical circuitry. The power supply includes a batteryreceiving region adapted to receive a second battery, means fordetermining a state of charge of the first battery, electrical circuitmeans operatively connected to the second battery for supplyingelectrical energy to the first electrical circuitry and to the firstbattery, means for receiving a signal indicative of the time varyingelectrical load current, and an electrical connector disposedelectrically between the second battery and the first electricalcircuitry. The electrical circuit means produces an output which is afunction of the state of charge of the first battery and the timevarying electrical load current.

According to still another aspect of the present invention, an apparatusincludes a battery powered device and a power supply. The batterypowered device includes a first housing which defines a first batteryreceiving region adapted to receive a first, rechargeable battery, andfirst electrical circuitry disposed in the first housing which receiveselectrical energy from the first battery and draws a time varyingelectrical load current. The battery powered device also includes meansfor providing an electrical signal indicative of the time varyingelectrical load current, and a first electrical connector operativelyelectrically connected to the first battery, the first electricalcircuitry, and the means for providing. The power supply includes asecond housing which defines a second battery receiving region adaptedto receive a second battery, means for receiving the signal, and powersupply circuitry disposed in the second housing. The power supplycircuitry receives electrical energy from the second battery, generatesan output for supplying energy to the first electrical circuitry and thefirst battery, and adjusts the output as a function of the state ofcharge of the first battery and the signal. The power supply alsoincludes a second electrical connector carried by the second housing.The second electrical connector is operatively electrically connected tothe power supply circuitry and the means for receiving.

Those skilled in the art will recognize still other aspects of thepresent invention upon reading and understanding the attacheddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 depicts an output current provided by a prior art device.

FIG. 2 is an electrical block diagram of an auxiliary power supplyconnected to a battery powered device.

FIG. 3 is a functional block diagram of an electrical device.

FIG. 4 is a functional block diagram of an auxiliary power supply.

FIG. 5 depicts an output current provided by an auxiliary power supply.

FIG. 6 depicts an auxiliary power supply and a mobile telephone.

FIG. 7 depicts an auxiliary power supply and a portable entertainmentdevice.

FIG. 8 depicts steps in the operation of an auxiliary power supply inconjunction with a battery powered device.

DETAILED DESCRIPTION

With reference to FIG. 2, a battery powered device 100 includes deviceelectrical circuitry 102, one or more main batteries 104, charge controlcircuitry 106, and a main device electrical connector 108 a.

The electrical circuitry 102 performs some or all of the functionalityprovided by the battery powered device 100. Depending on the type ofelectrical device 100, the electrical circuitry 102 may take any numberof forms. For example, the electrical circuitry 102 may perform theelectrical functions required of a camera, PDA, mobile phone, gamedevice, bar code reader, computer mouse or keyboard, portable or remotecommunications device, or the like, although other types of devices 100and electrical circuitry 102 are contemplated.

The device circuitry 102 may also include a communications interface 103adapted to provide communications with an external device or devices. Inone embodiment, the communications interface is a known universal serialbus (USB) communications interface which provides digital communicationswith external devices, for example an external computer. Other serial,parallel, or analog communications interfaces are also contemplated.

In normal operation, the electrical circuitry 102 is powered by one ormore main batteries 104. The chemistry, form factor, and number of thebatteries 104 employed in a given device 100 are generally dependent onthe type of device 100 and the requirements of the electrical circuitry102. In many cases, however, the battery or batteries 104 are secondarybatteries. Examples of currently available secondary battery chemistriesLi-ion, nickel metal hydride (NiMH), nickel cadmium (NiCd), Li-ionpolymer, and reusable alkaline. Commonly available battery form factorsinclude generally cylindrical batteries such as conventional AAA, AA, C,and D size cells, as well as generally rectangular or prismaticbatteries. The main battery 104 may also be a so-called smart batterywhich operates according to the known smart battery standard. Otherbattery chemistries and form factors are also contemplated.

The charge control circuitry 106, which provides functionality relatedto the charging of the main battery or batteries 104, is disposedelectrically between the electrical connector 108 and the battery 104.In an implementation which is particularly well suited to devices 100 inwhich the bulk of the charge control functionality is located externalto the device 100, the charge control circuitry includes a diode,transistor, or components which protects the device 100 if the maindevice connector 108 a is shorted, connected to external signals of theincorrect polarity, subjected to an over voltage, or the like. Inanother implementation, the charge control circuitry 102 may includecircuitry which controls the voltage and/or current applied to thebattery or batteries 104. Such circuits, which commonly receive powerfrom a power cube connected to the AC mains or an automotive 12 VDCpower source, are known to those skilled in the art and are ordinarilyimplemented based on the desired charging functionality and thecharacteristics of the battery 104. The charge control circuitry 106 mayalso be omitted. Some or all of the charge control circuitry 106, thedevice electrical circuitry 102, and the communications interface (103)may be implemented in a single integrated circuit or applicationspecific integrated circuit (ASIC); they may also be implemented inmultiple integrated circuits or discrete components.

The main device electrical connector 108 a provides removable electricalconnections between the device 100 and the external environment. In theexemplary USB interface, the connector 108 a is a standard USB connectorwhich provides positive 110 _(p) and negative 110 _(n) electrical powerconnections, as well as positive 112 _(p) and negative 112 _(n) dataconnections. The main device connector 108 a may also provide otherelectrical connections relevant to the particular device 100, such asdata or memory connections, control connections, or the like. The maindevice connector 108 a may also be implemented as one more physicalconnectors; such a configuration is particularly useful where it isdesirable to allow the device 100 to be independently connected to morethan one external device.

With ongoing reference to FIG. 2, the total current I_(out) received bythe battery powered device 100 through the electrical connector 108 acan be expressed as follows:I _(out) =I _(device) +I _(battery)   Equation 1where I_(device) is the load current drawn by the device circuitry 103and I_(battery) is the current drawn by the main battery 104. To measurethe device load current I_(device), a sense resistor 116 may be disposedelectrically in series between the device electrical circuitry 102 andthe negative 110 _(n) or positive 110 _(p) power connections. As will beappreciated, the voltage across the sense resistor 116 provides a signal114 indicative of the load current drawn by the device electricalcircuitry 102. The current drawn by the main battery 104 could likewisebe determined using an analogous sense resistor in series with thebattery 104.

Turning now to FIG. 3, the device circuitry 102 typically includes aprocessor 202 such as a microprocessor or microcontroller which executesinstructions in an associated memory. The processor 202 coordinates thetransfer of data via the communications interface 103 and cooperateswith the other device specific circuitry 204 to provide the desireddevice functionality. The processor 202 also receives informationrelating to or otherwise controls factors which influence one or more ofthe device electrical load 206, the device electrical characteristics208, and the main battery state of health 210.

The device electrical load information 206 includes informationindicative of one or more of the actual or anticipated powerrequirements of the device electrical circuitry 102. The measured load212 includes a measured value of the load presented by the deviceelectrical circuitry 102. In one implementation, the measured load isthe value of I_(device) obtained by measuring the voltage across thesense resistor 116.

The actual operating state information 214 includes information relatingto the current operating state or mode of the device 100. For example,many devices are characterized by relatively long periods of relativelylow power or quiescent operation interspersed with periods of relativelyhigher power operation. Depending on the nature of the device, thedevice typically enters a particular operating state in response to anoperator input or command or automatically based on another event orcriterion. In the case of a mobile telephone, for example, the user mayinitiate or accept a telephone call, during which time the circuitry 102places a relatively high load on the main battery 104. Moreover, thepower output of the telephone's transmitter may be adjusted based on thestrength of the local radio frequency signal, again influencing loadplaced on the main battery 104. In any case, the operating state orstates 214 of the device may in many cases provide a reasonableindication of the load presented to the main battery 104.

The anticipated operating state information 216 includes informationrelating to an anticipated or predicted operating state of the device100. A portable or remote data communications device, for example, maybe programmed to upload or download data at one or more scheduled timesduring the course of day, week, or other time period. The device 100 mayalso be programmed to transfer data at desired time intervals (e.g.,hourly, daily, or the like), or following the occurrence of certainevents. The device 100 may also be programmed to predict futureoperating states based on the operating history of the device, forexample where the user has caused the device to enter a particularoperating state at regular times or intervals. In any case, theanticipated operating state 216 may provide a reasonable indication ofan anticipated future operating state, and hence an anticipated load tobe presented to the main battery 104.

The device electrical characteristics 208 include information relatingto the power requirements of the device 100. In one implementation, adevice identifier 218 or code is stored in a memory associated with thedevice 100. As one example, the device identifier 218 identifies themanufacturer and model number of the device 100. As another example, thedevice identifier 218 may identify the device 100 as belonging to aclass of devices having similar power requirements. Analogously, abattery identifier 220 may also be used to identify the manufacturerand/or model number of the main battery 104, or otherwise identify thebattery as being of a particular class of batteries having similarcharacteristics. In another implementation, specific battery voltage,current, capacity, chemistry or other characteristics 222 of the device100 may be provided, either in a memory associated with the device 100or a memory associated with the main battery 104.

The battery state of health 210 includes information indicative of thehealth of the main battery 104. This information may include informationindicative of the battery charge state 224, for example the measuredoutput voltage V_(main) of the main battery 104. In another example, thecharge state may be determined by way of a so called fuel gauge, inwhich the charge remaining in the main battery is estimated based on thecapacity of the battery and a measurement or estimate of the energydrawn from it. Another example of battery health information 210 is abattery temperature 226, which is typically measured using a thermistorof other temperature sensitive device.

Returning now to FIG. 2, a battery powered auxiliary power supply 150includes one or more auxiliary batteries 152, power supply circuitry154, and an auxiliary electrical connector 108 b. In one embodiment, andas will be described in greater detail below, the auxiliary power supply150 is adapted to interface with a number of different main devices 100having different electrical power requirements. In another embodiment, afamily of external power supplies is provided, with the members of thefamily having different load ratings or capacities.

The auxiliary power supply 150 includes a battery receiving region whichincludes the requisite battery contacts and which accepts one or moreauxiliary batteries 152. The chemistry, form factor, and number of theauxiliary batteries 152 employed in a given power supply 150 aregenerally dependent on the power requirements of the main device ordevices 100 with which the external power supply 150 is expected tooperate, the desired form factor and portability of the external powersupply 150, and like factors.

The power supply circuitry 154, which is powered by the auxiliarybattery 152, provides electrical energy for powering the deviceelectronics 102 and charging the main battery 104. Also associated withthe auxiliary power supply 150 is a communication interface 156. In theillustrated embodiment, the communication interface 156 is a USBinterface, although the interface would ordinarily be selected forcompatibility with the device or devices 100 with which the auxiliarypower supply 150 is expected to operate. Note that the charge controlcircuit 154 and communications interface 156 may be implemented in oneor more integrated circuits, ASICs, or other devices.

A sense resistor 120 analogous to the sense resistor 116 provides asignal indicative of the output current I_(out) being supplied to thebattery powered device 110.

The power supply connector 108 b is adapted to matingly engage thebattery powered device connector 108 a to provide the power 110 _(p),110 _(n) and data 112 _(p), 112 _(n) connections.

Turning now to FIG. 4, the power supply circuitry 154 includesadvantageously includes a processor 302 such as a microprocessor ormicrocontroller which executes instructions stored in an associatedmemory. The processor 302 interfaces with the communications interface156 and with power supply electronics 304, and also receives informationrelating to one or more of the battery powered device electricalcharacteristics 306, the battery powered device operating state 308, andmain battery state of health 310.

The battery powered device electrical information 306 includesinformation relating to the power and/or load requirements various maindevices 100. In one implementation, the voltage, current, or othercharacteristics of various battery powered devices 100 are contained ina list or database stored in a memory accessible to the processor 302.The device identifier 218 received from a given main device is used toaccess the relevant information from the memory. In anotherimplementation, the characteristics of various main batteries 104 arestored, with the battery identifier 220 received from a given maindevice used to access the relevant information. As will be appreciated,these arrangements facilitate the use of the external power supply 150with battery powered devices 100 or batteries 104 having different powerrequirements.

The main device operating state information 308 includes informationrelating to the operating states or modes of one or more battery powereddevices 100. In one implementation, the voltage, current, or other loadrequirements associated with the operating states of one or more batterypowered devices 100 are included in a list or database stored in thememory. The actual 214 or anticipated 216 operating state informationand the device identifier 218 identifier, if applicable, received from agiven device 100 are used to access the pertinent information from thememory. Note that some or all of the device electrical characteristics306 and operating state information 308 may be combined in a single listor database. In the mobile telephone described above, for example, thetelephone may include a low power or idle mode and one or more transmitmodes, each presenting a different electrical load. Other devices 100may have different operating modes. As will be appreciated, the actualoperating state 216 information may serve as a proxy for the measuredload 212. Moreover, the anticipated operating state information 216provides information which is ordinarily not available or oftendifficult to infer from the measured load 212 or the actual operatingstate 216.

The main battery state of health 310 includes main battery state ofhealth 210 information received from the battery powered device 100, forexample the main battery voltage V_(main). In the embodiment of FIG. 2,the main battery voltage can ordinarily determined form the voltage atthe positive power connection 110 _(p). Alternately, the voltage may beobtained from another location. While the main battery state of healthinformation 310 is shown as being provided directly to the power supplyelectronics 304, the information may also be communicated to theprocessor 302 via the communications interface 156.

The processor 302 is operatively connected to the power supplyelectronics 304. Various power supply circuits and topologies are knownand can be readily implemented by those skilled in the art based onfactors such as electrical characteristics of the battery powered deviceand its batteries. Advantageously, however, the voltage, current, and/orother output characteristics of the power supply electronics 304 areestablished based on information received from the processor 302. Inparticular, the processor 302 establishes the voltage and/or currentsetpoints of the power supply electronics 304 as a function of one ormore of the device electrical characteristics 306, the device operatingstate information 308, and the main battery state of health 310.

The auxiliary battery state of health information 312 includesinformation relevant to the state of health of the auxiliary battery152. Such information may include charge state information 324 such as ameasured auxiliary battery voltage V_(aux), the auxiliary batterytemperature 326 or other information analogous to that described abovein relation to the main battery 104. While the auxiliary battery stateof health information 312 is shown as being provided directly to thepower supply electronics 304, the information may also be provided tothe processor 302.

In one implementation, the power supply electronics 304 can beconfigured to supply a total output current I_(out) to the batterypowered device 100 according to the transfer function of FIG. 1, wherethe output current I_(out) is a function of the auxiliary batteryvoltage V_(aux) and the main battery voltage V_(main).

However, the energy available from the auxiliary battery 154 may be moreeffectively utilized by varying or modulating the output of the externalpower supply 150 as a function of the actual or predicted load presentedby the device electronics 102. FIG. 5 depicts the output current I_(out)supplied by the power supply electronics 304 as a function of the mainbattery voltage V_(main) for each of a plurality of device electricalcircuit currents I_(device), with I_(device) generally increasing fromI₀ to I₆, and where I₀ represents the load current with the device 100turned off or in a relatively low power operating mode. In FIG. 5, theauxiliary battery voltage V_(aux) is assumed to be constant for ease ofillustration, it being understood that the output current I_(out) ispreferably also a function of the auxiliary battery voltage V_(aux) asdepicted generally in FIG. 1.

As can be seen, the output current supplied by the power supplyelectronics 304 is, for a given device electrical load I_(device) andauxiliary battery voltage V_(aux), at a maximum value where the mainbattery voltage V_(main) is relatively low. The maximum output currentI_(out max) is advantageously set at a value which satisfies thefollowing condition:I _(battery0) +I _(device) >I _(out max) ≧I _(device)   Equation 2where I_(battery0) is the charge current that would be drawn by the mainbattery 104 if the current were not otherwise limited.

Such an arrangement assures that the external power supply 150 providessufficient power to operate the battery powered device 100 while stillproviding energy to charge the main battery 104, albeit at a reducedrate. As discussed more fully above, the device current I_(device) maybe advantageously obtained by measuring the actual device current orinferred from an actual operating state of the battery powered device100.

The maximum output current I_(out max) may also be adjusted based on thevalue of an anticipated device operating state. Thus, where it isexpected that the device will become active at a time in the future, themaximum output current may be increased to a level which charges themain battery as quickly as possible, or to a level which is expected tofully charge the main battery 104 before the device 100 enters thehigher power operating state. As another example, the user may enter acommand to charge the main battery 104 as quickly as possible orotherwise at a relatively faster rate, in which case the value of themaximum output current may be increased accordingly.

The output current I_(out) can be adjusted by causing the processor 302to vary the value of the sense resistor 120 as a function of the devicecurrent I_(device). As will be appreciated, the current feedback isfunction of the value of the sense resistor 120. Consequently;decreasing the value of the sense resistor 120 increases the outputcurrent, while increasing the value decreases the output current. Asdiscussed above, the value of the sense resistor may advantageously belimited to values at which Equation 2 is satisfied. As a result, theoutput current can be reduced to or held a level that is below the sumof the maximum charge acceptance rate for the main battery 104 and theload presented by the device electrical circuitry 102. Other techniques,such as the use of a programmable gain amplifier at the output of thesense resistor 120, may also be implemented.

The power supply electronics 304 may be implemented using the knownTEC103 Step-Up Converter and Charge Controller integrated circuitavailable from Techtium, Ltd. of Tel Aviv, Israel. Other circuits andcircuit configurations are also contemplated.

Various alternatives are possible. As will be appreciated, the functionsimplemented in the auxiliary power supply 150 ordinarily depend on thecharacteristics of or other information available from the batterypowered device or devices 100 with which the auxiliary power supply 150is expected to operate.

Moreover, the battery powered device 100 may also supply the deviceelectrical load information 206 through a signal available at theconnector 108 a. In one implementation, a measured value of the devicecurrent I_(device) may be provided via an analog voltage signal. Inanother, the actual 214 or anticipated 216 operating state informationmay be provided via a digital signal. In yet another, the desiredsignals may be provided in a two wire communications interface in whichthe signals are superimposed on the power signal, preferably as serialdigital signals generated by modulating the voltage and/or currentlevels. In still another, the battery powered device 100 may supply anoutput current set point signal which is a function of the devicecurrent. In any case, the auxiliary power supply circuitry 154 includessuitable analog and/or digital circuitry for adjusting the value theoutput current I_(out) as a function of the signal, for example theadjusting the effective value of the sense resistor 120.

As another alternative, the auxiliary battery 152 may be located in theauxiliary power supply 150, with some or all of the power supplycircuitry 154 located in the battery powered device 100.

The above discussion has focused on providing information which isdirectly indicative of the load presented by the device electronics 102.In view of Equation 1, however, information indicative of the mainbattery current I_(battery) may be provided, as subtracting the batterycurrent I_(battery) from the output current I_(out) yields informationindicative of the load presented by the device electronics 102.

Turning now to FIG. 6, an exemplary auxiliary power supply 650 is shownwith a mobile telephone 600. The phone 600 includes a housing 601 havinga front major surface 602, a spaced apart rear major surface, andadditional surfaces 604 a, 604 b, 604 c, and 604 d. Located on thesurface 604 a is a female connector 608 a.

The auxiliary power supply 650 includes a housing 651 having a frontmajor surface 672, a spaced apart rear major surface, and additionalsurfaces 674 a, 674 b, 674 c, and 674 d. The auxiliary power supply 650houses the power supply circuitry 154 and includes a battery receivingregion which is adapted to selectively receive an auxiliary battery 652.A user removable cover 660 (shown in partial cutaway view to expose thebattery 652) allows the user to selectively access the battery receivingregion. A male connector 608 b located on the surface 674 a is adaptedto matingly engage the female connector 608 a. As illustrated, thecurvature of the surface 674 a substantially conforms to a curvature ofthe surface 604 a, and the width of the housing 601 is approximatelyequal to the width of the housing 601 at the interface therebetween.

Turning now to FIG. 7, another exemplary auxiliary power supply 750 isshown with a portable entertainment device 700. The portableentertainment device 700 includes a housing 701 having a front majorsurface 702, a spaced apart rear major surface, and additional surfaces704 a, 704 b, 704 c, and 704 d. Located on the surface 704 a is a femaleconnector 708 a.

The auxiliary power supply 750 includes a housing 751 having a frontmajor surface 772, a spaced apart rear major surface, and additionalsurfaces 774 a, 774 b, 774 c, and 774 d. The auxiliary power supply 750houses the power supply circuitry 154 and includes a battery receivingregion which contains the requisite positive and negative batteryterminals and is adapted to selectively receive auxiliary batteries 752.A user removable cover 760 (shown in partial cutaway view to expose thebatteries 752) allows the user to selectively access the batteryreceiving region. A male connector 708 b located on the surface 774 a isadapted to matingly engage the female connector 708 a. As illustrated,the width of the housing 701 is approximately equal to the width of thehousing 701 at the interface therebetween.

Other arrangements are also possible. For example, the auxiliary powersupply may connect to one of the other surfaces of the main device. Theauxiliary power supply and the device may also connect via a cable whichincludes suitable connectors, and may also have a cylindrical or otherform factor which does not conform to that of the battery powereddevice.

In operation, the user operates the battery powered device 100 asdesired. Of course, continued operation of the device 100 leads to theeventual discharge of the main battery 102. To recharge the battery, theuser typically connects the device to a fixed charger.

In some situations, such as where a power source required to operate thefixed charger is not readily available, the user may elect to use theexternal power supply 150. With reference to FIG. 8, the user connectsthe external power supply 150 and the battery powered device 100 throughtheir corresponding electrical connector portions 108 a, 108 b at step802.

Where the auxiliary power supply 150 and the main device 100 communicatethrough a USB interface, the devices undergo a USB enumeration processat 804. Once the external power supply 150 is identified as an externalpower source, the battery powered device may advantageously allow itscommunication interface 103 to operate outside the USB power standards.

If implemented, the battery powered device 100 provides the deviceelectrical characteristics 208 to the external power supply 150 at step806. At 808, the external power supply 150 uses the device powercharacteristic 208 to establish the desired voltage and current levelsto be applied to the battery powered device 100.

At 810, the battery power device 100 provides the device electrical loadinformation 206 to the external power supply 150. As noted above, theload information 206 may be provided by way of a measured value 212.Alternately, or in addition to the measured value 212, actual 214 and/oranticipated 216 operating state information may be transferred.Depending on the implementation, the information may be providedcontinuously or at various times during operation.

At 812, the auxiliary power supply 150 supplies an output voltage andcurrent to the main device. As noted above, the power supply output ispreferably a function of the electrical load presented by the deviceelectrical circuitry 103.

At 814, the user disconnects the auxiliary power supply 150 from themain device.

The invention has been described with reference to the preferredembodiments. Of course, modifications and alterations will occur toothers upon reading and understanding the preceding description. It isintended that the invention be construed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims.

1. An auxiliary power supply for use with a battery powered deviceincluding first electrical circuitry which presents a time varyingelectrical load and a first rechargeable battery which provideselectrical energy to the first electrical circuitry, the auxiliary powersupply comprising: a battery receiving region adapted to receive asecond battery; second electrical circuitry, wherein the secondelectrical circuitry receives a signal from the battery powered device,which signal is indicative of the magnitude of the time varyingelectrical load, wherein the second electrical circuitry utilizes energyfrom the second battery to produce a power supply output (110 _(p), 110_(n)) for recharging the first rechargeable battery and for providingelectrical energy to the first electrical circuitry, and wherein thesecond electrical circuitry adjusts the power supply output as afunction of the charge state of the first rechargeable battery, thecharge state of the second battery, and the signal; a first electricalconnector in operative communication with the second electricalcircuitry and adapted to selectively electrically connect the powersupply output to the battery powered device.
 2. The power supply ofclaim 1 wherein the signal includes a measured value of the time varyingelectrical load.
 3. The power supply of claim 2 wherein the measuredvalue of the time varying electrical load includes a measured value ofan electrical load current, and wherein the second electrical circuitryadjusts the power supply output current as a function of the firstrechargeable battery voltage, the second battery voltage, and themeasured value of the time varying electrical load current.
 4. The powersupply of claim 3 wherein the second electrical circuitry maintains thepower supply output current at a level which is substantiallyindependent of the first rechargeable battery voltage when the firstrechargeable battery voltage is below a first voltage, and wherein thelevel is a function of the measured value of the time varying electricalload current and the second battery voltage.
 5. The power supply ofclaim 1 wherein the battery powered device has at least a firstoperating mode in which the first electrical circuitry presents a firstelectrical load and a second operating mode in which the deviceelectrical circuitry presents a second electrical load which isdifferent from the first electrical load, and wherein the signalincludes the operating mode.
 6. The power supply of claim 1 wherein thesecond electrical circuitry includes a digital interface in operativecommunication with the first electrical connector and wherein the signalis received via the digital interface.
 7. The power supply of claim 6wherein the digital interface is a USB interface.
 8. The power supply ofclaim 6 wherein the power supply receives information indicative of thecharge state of the first rechargeable battery via the digitalinterface.
 9. The power supply of claim 1 wherein the battery powereddevice includes a first housing having spaced apart first and secondmajor surfaces and a third surface having a first length, wherein thebattery powered device includes a second electrical connector disposedon the third surface of the first housing, and wherein the power supplyincludes a second housing having spaced apart first and second majorsurfaces and a third surface having a second length, wherein the firstelectrical connector is disposed on the third surface of the secondhousing and adapted to matingly engage the second electrical connector,and wherein second length is less than or equal to the first length. 10.An apparatus for supplying electrical energy to a battery powered deviceincluding a first, rechargeable battery and first electrical circuitry,wherein the first electrical circuitry receives electrical energy fromthe first battery and presents a time varying electrical load currentduring operation of the device, the apparatus comprising: a firsthousing which defines a battery receiving region; first and secondbattery contacts for making electrical contact with a second batteryreceived in the battery receiving region; a first electrical connectorin mechanical communication with the first housing and disposedelectrically between the second battery and the first electricalcircuitry; second electrical circuitry, wherein the second electricalcircuitry receives energy from the second battery, generates an outputfor supplying electrical energy to the first electrical circuitry andfor recharging the first battery, and adjusts the output as a functionof the state of charge of the first battery and a signal indicative ofthe time varying electrical load current.
 11. The apparatus of claim 10wherein the signal is an analog voltage signal.
 12. The apparatus ofclaim 10 wherein the signal is a digital signal.
 13. The apparatus ofclaim 12 wherein the signal is superimposed on the output.
 14. Theapparatus of claim 12 wherein the battery powered device has at least afirst operating mode in which the first electrical circuitry draws afirst electrical load current and a second operating mode in which thefirst electrical circuitry draws a different second electrical loadcurrent, and wherein the digital signal is indicative of an anticipatedoperating mode of the battery powered device.
 15. The apparatus of claim12 wherein the second electrical circuitry is disposed in the firsthousing and wherein the first electrical connector is disposedelectrically between the second electrical circuitry and the firstelectrical circuitry.
 16. The apparatus of claim 10 further including adigital communications interface and wherein information indicative ofthe state of charge of the first battery and the signal are received viathe digital communications interface.
 17. The apparatus of claim 10wherein the output current is limited to a value which satisfies therelationshipI _(battery0) +I _(device) >I _(out) where I_(out) is the value of theoutput current, I_(device) is the time varying electrical load current,and I_(battery0) is a current which would be drawn by the first batteryif the output current were not limited.
 18. The apparatus of claim 10wherein the battery powered device includes a second housing havingfirst and second major surfaces, a curved third surface, and a secondelectrical connector located on the third surface, and wherein the firsthousing includes fourth and fifth major surfaces, a sixth surface,wherein the first electrical connector is located on the sixth surfaceand adapted to selectively connect to the second electrical connector,wherein the sixth surface has a curvature which substantially conformsto the curvature of the third surface.
 19. A power supply for a batterypowered device including first electrical circuitry which presents atime varying electrical load current and a first, rechargeable batterywhich supplies electrical energy to the first electrical circuitry, thepower supply comprising: a battery receiving region adapted to receive asecond battery; means for determining a state of charge of the firstbattery; means for receiving a signal indicative of the time varyingelectrical load current; electrical circuit means operatively connectedto the second battery for supplying electrical energy to the firstelectrical circuitry and to the first battery, wherein the electricalcircuit means produces an output which is a function of the state ofcharge of the first battery and the time varying electrical loadcurrent; an electrical connector disposed electrically between thesecond battery and the first electrical circuitry.
 20. The power supplyof claim 19 wherein the means for receiving includes a serialcommunications interface.
 21. The power supply of claim 19 furtherincluding a memory which contains information indicative of theelectrical characteristics of a plurality of battery powered devices,and wherein the output is a function of the information.
 22. The powersupply of claim 19 further including a memory which contains informationindicative of the electrical characteristics of a plurality ofbatteries, and wherein the output is a function of the information. 23.The power supply of claim 19 further including a memory which containsinformation indicative of the operating modes of a plurality of batterypowered devices, and wherein the output is a function of theinformation.
 24. The power supply of claim 19 wherein the batterypowered device includes a plurality of rechargeable batteries whichsupply electrical energy to the first electrical circuitry and thebattery receiving region is adapted to receive a plurality of batteries.25. An apparatus comprising: a battery powered device including: a firsthousing which defines a first battery receiving region adapted toreceive a first, rechargeable battery; first electrical circuitrydisposed in the first housing, wherein the first electrical circuitryreceives electrical energy from the first battery and draws a timevarying electrical load current; means for providing an electricalsignal indicative of the time varying electrical load current; a firstelectrical connector operatively electrically connected to the firstbattery, the first electrical circuitry, and the means for providing; apower supply including: a second housing which defines a second batteryreceiving region adapted to receive a second battery; means forreceiving the signal; power supply circuitry disposed in the secondhousing, wherein the power supply circuitry receives electrical energyfrom the second battery, generates an output for supplying energy to thefirst electrical circuitry and the first battery, and adjusts the outputas a function of the state of charge of the first battery and thesignal; a second electrical connector carried by the second housing andoperatively electrically connected to the power supply circuitry and themeans for receiving.
 26. The apparatus of claim 25 wherein the means forreceiving includes a digital communications interface.
 27. The apparatusof claim 26 wherein the digital communications interface is a serialinterface.
 28. The apparatus of claim 25 wherein the battery powereddevice has at least a first operating state in which the firstelectrical circuitry draws a first electrical current and a second statein which the second electrical circuitry draws a different secondelectrical current, and wherein the signal is indicative of theoperating state.
 29. The apparatus of claim 28 wherein the signal isindicative of an anticipated operating state.
 30. The apparatus of claim25 wherein the output includes an output current, wherein the outputcurrent is a function of the state of charge of the first battery whenthe first battery is relatively more charged and substantiallyindependent of the state of charge of the first battery when the firstbattery is relatively less charged.
 31. The apparatus of claim 25wherein the signal is superimposed on the output.